Drilling motors are used as part of a drill string, near the drill head, to drive the drill head rotationally relative to the upwardly continuing drill string. The drilling fluid flow is usually used to power the motor.
Drilling motors are often used on coiled tubing which cannot be rotated. In some cases the motor is used to rotationally attach the drill string to hardware down hole that is to be recovered by tension forces. Jars are sometimes used to deliver shock to the hardware. Motors that are designed for drilling are sometimes not designed to accept axial shock forces.
Motors used for drilling in open holes drive bits that can become stuck in the hole and require axial thrust along the drill string for recovery. Jars can provide shock to the stuck bit to free a bit not recoverable without jars. To benefit from the application of jars, motors need to withstand the shock applied.
Axial shock loads imposed upon motors can separate their output drive shafts. The usual structure of motors includes capture rings that will extract all of the output shaft when the damaged motor is removed from the well. The separation experience, however, ends the usefulness of the motor as a rotational drive, until it is removed and repaired. There is a need for apparatus in the motor to accept shock loads, even if the motor is not running when the shock loads are applied, yet allow the motor to continue in service when the shock loads are no longer being applied.